The present invention relates to a device for delivering nitric oxide into the breathing gases of a patient that is modular in nature. The device may be used to advantage to maintain nitric oxide therapy when a patient is being transported from one location to another location.
Nitric oxide (NO) is a gas that, when inhaled, acts to dilate blood vessels in the lungs, improving oxygenation of the blood and reducing pulmonary hypertension. For this purpose, the nitric oxide is provided in the inspiratory breathing gases for the patient. The dosages of nitric oxide are small, typically 100 parts per million (ppm) or less.
In many cases, the inspiratory breathing gases for the patient will be provided by a gas delivery system such as a mechanical ventilator. U.S. Pat. No. 5,558,083 shows apparatus for administering NO into the inspiratory breathing gases provided by a mechanical ventilator. The apparatus includes a connection to a NO supply conduit inserted in the inspiratory limb of a patient breathing circuit connected to the ventilator. The NO supply conduit is connected through a controllable metering valve to a supply of NO containing gas. Flow sensors are provided in the NO supply conduit and in the inspiratory limb upstream of the NO supply conduit connection. The flow sensors are connected to a control that operates the metering valve based on the dosage of NO desired for the patient and the gas flows sensed by the concentration sensor. An analytical gas flow sensor is provided downstream of the NO supply conduit connection in the patient breathing circuit to analyze properties of the inspiratory breathing gases being supplied to the patient. The apparatus of the '083 patent provides a generally continuous flow of NO containing gas during the supply of breathing gases to the patient. It is also possible to provide a discrete pulse of NO containing gas at a predetermined time in the inspiratory phase of the patient's breathing cycle.
In a commercial embodiment, NO delivery apparatus of the type described above is typically available as a stand alone unit that is used in conjunction with a breathing gas delivery system when NO therapy is desired for a patient. For this purpose, the breathing gas flow sensor, the nitric oxide supply conduit connection, and the gas analyzer sampling port may be provided in a common housing that can be inserted in the inspiratory limb of the breathing circuit. For best performance, the gas analyzer sample part is placed at a distance from the NO injection point to allow for proper gas mixing. Also, the gas sample point is normally positioned close to the inspiratory side of the wye connector to most accurately sense the level of NO2 being produced. The commercial embodiment provides the advantage of allowing the apparatus to be used with a variety of different breathing gas delivery systems without being restricted to a particular model or to the products of a particular manufacturer.
However, the stand alone unit tends to be somewhat bulky. It is preferable to keep the NO supply conduit short and to administer the NO into the inspiratory breathing gases close to the patient to avoid/limit a reaction between the NO and oxygen in the breathing gases that leads to the production of toxic nitrogen dioxide in the breathing gases. This often means that the NO delivery apparatus is proximate to the patient and is in the way of other apparatus or attending patient caregivers. Also, with such apparatus, it may be difficult to maintain NO therapy when transporting a patient from one location to another as, for example, from an intensive care unit to a regular hospital room.